1. Field of the Invention
The present invention relates to a driving method for a solid-state imaging device configured to include: a plurality of photoelectric conversion elements formed on a semiconductor substrate; a plurality of vertical charge transfer parts that transfer electric charges generated in the plurality of photoelectric conversion elements in the vertical direction; a line memory that temporarily stores the electric charges transferred from the plurality of vertical charge transfer parts; and a horizontal charge transfer part that transfers the electric charges stored in the line memory in the horizontal direction perpendicular to the vertical direction.
2. Description of the Related Art
The related-art solid-state imaging device in which low-sensitivity photoelectric conversion elements, which are arrayed in a square lattice and have low detection sensitivity, and high-sensitivity photoelectric conversion elements, which are arrayed in a square lattice and have high detection sensitivity, are alternately disposed on a silicon substrate so as to be adjacent to each other and shifted from each other such that a honeycomb-like array pattern is formed is proposed in JP-A-2004-055786, for example.
The detection sensitivity of a photoelectric conversion element refers to a property indicating how many signals can be taken out from the photoelectric conversion element when a predetermined amount of light is incident on the photoelectric conversion element. That is, it can be defined that a high-sensitivity photoelectric conversion element having relatively high sensitivity has a property that a larger amount of signals can be taken out when the same amount of light is incident than a low-sensitivity photoelectric conversion element having relatively low sensitivity. In the case of the high-sensitivity photoelectric conversion element, a large amount of signals can be obtained with a small amount of light. Accordingly, the high-sensitivity photoelectric conversion element is most appropriate for photographing a photographic subject under low luminance. However, a signal is immediately saturated when a large amount of light is incident on the high-sensitivity photoelectric conversion element, and accordingly, the high-sensitivity photoelectric conversion element is not suitable for photographing the photographic subject under high luminance. On the other hand, in the case of the low-sensitivity photoelectric conversion element, a large amount of signals cannot be obtained even if a large amount of light is incident. Accordingly, the low-sensitivity photoelectric conversion element is most appropriate for photographing a photographic subject under high luminance. However, the amount of signals obtainable is too small when a small amount of light is incident, and accordingly, the low-sensitivity photoelectric conversion element is not suitable for photographing the photographic subject under low luminance.
In a solid-state imaging device disclosed in JP-A-2004-055786, a dynamic range can be extended by mixing a low-sensitivity signal obtained from a low-sensitivity photoelectric conversion element and a high-sensitivity signal obtained from a high-sensitivity photoelectric conversion element.
As methods of mixing signals, a method in which a low-sensitivity signal and a high-sensitivity signal are separately read and are then mixed in a subsequent-stage signal processing unit and a method of adding a low-sensitivity electric charge generated in a low-sensitivity photoelectric conversion element and a high-sensitivity electric charge generated in a high-sensitivity photoelectric conversion element at the time of transfer are considered. A method of adding a low-sensitivity electric charge and a high-sensitivity electric charge corresponding to the same color components and transferring the added electric charges in a solid-state imaging device having the configuration disclosed in JP-A-2004-055786 will be described with reference to FIG. 6.
FIG. 6 is a view explaining the related-art driving method in a case of performing addition of electric charges in a solid-state imaging device having the configuration disclosed in JP-A-2004-055786.
Referring to FIG. 6, a solid-state imaging device includes a plurality of VCCDs, an HCCD, and a line memory provided between the plurality of VCCDs and the HCCD. In addition, the line memory is driven by a driving pulse LM having a high level (hereinafter, simply referred to as ‘H’) or a low level (hereinafter, simply referred to as ‘L’), and the HCCD is driven in a four phase by driving pulses φH1 to φH4 each having an ‘H’ or an ‘L’. Moreover, an electrode to which the driving pulse φH1 is supplied, an electrode to which the driving pulse φH2 is supplied, an electrode to which the driving pulse φH3 is supplied, and an electrode to which the driving pulse φH4 is supplied among electrodes included in the HCCD are expressed as H1, H2, H3, and H4, respectively. In addition, among electric charges obtained from high-sensitivity photoelectric conversion elements, an electric charge corresponding to a red component is expressed as ‘R’ and an electric charge corresponding to a green component is expressed as ‘G’. In addition, among electric charges obtained from low-sensitivity photoelectric conversion elements, an electric charge corresponding to a red component is expressed as ‘r’ and an electric charge corresponding to a green component is expressed as ‘g’.
Electric charges transferred from the plurality of VCCDs are stored in the line memory, and then the driving pulses φH1 and φH3 are changed to ‘l’ at time t1 and the driving pulse φLM is changed to ‘L’ at time t2 such that the low-sensitivity electric charges ‘r’ and ‘g’ are transferred to transfer channels below the electrodes H1 and H3. Then, the driving pulse φLM is changed to ‘H’ at time t3 and then the driving pulses φH1 and φH3 are changed to ‘L’ and the driving pulses φH2 and φH4 are changed to ‘H’ at time t4, such that the electric charge ‘g’ positioned below the electrode H1 is transferred below the electrode H4 and the electric charge ‘r’ positioned below the electrode H3 is transferred below the electrode H2. Then, the driving pulse φLM is changed to ‘L’ at time t5, such that the high-sensitivity electric charges ‘R’ and ‘G’ are transferred to transfer channels below the electrodes H2 and H4. As a result, the electric charge ‘R’ is added to the electric charge ‘r’, and the electric charge ‘G’ is added to the electric charge ‘g’. After addition of the electric charges, the added electric charges are sequentially transferred by changing the driving pulse φLM to ‘H’ at time t5 and then switching the driving pulses φH1 to φH4 between ‘L’ and ‘H’.
In the driving method shown in FIG. 6, it is necessary to perform transfer of electric charges from a line memory to an HCCD twice in order to add the electric charges. Accordingly, in the case when the number of pixels increases, a frame rate decreases in the driving method described above.